An integrated circuit chip package typically comprises an encapsulated silicon wafer bearing an integrated circuit, and a lead frame. An integrated circuit is etched into the silicon wafer and includes a number of bond pads which may be positioned about a perimeter of the silicon wafer. The lead frame typically comprises a support structure for the silicon wafer and electrical leads or "pins" that may be used to form electrical connections between the lead frame and other electrical devices. Electrical connections are made between the integrated circuit and the lead frame by bonding a metallic wire, typically gold, to the bond pads of the integrated circuit and to the pins of the lead frame.
A wire bonding machine is typically used to bond the wire to the bond pads and lead frame pins. The bonding wire may be threaded through a capillary which is mounted to a transducer of the wire bonding machine. The transducer may be manipulated to move the capillary both vertically and horizontally. The transducer or another energy source, such as a hydrogen flame, is then used to apply energy to the end of the bonding wire which protrudes from an exit end of the capillary. This applied energy may cause the wire to soften or melt. The molten wire may form the shape of a ball which is placed on a target bond pad by manipulating the transducer to move the capillary.
The exit end of a wire bonding capillary is often referred to as the capillary face. Previous capillaries have had a circular face. A disadvantage of having a capillary with a circular face is that the spacing between bond pads may be limited by the space required for the capillary. If the bond pad spacing is too close, the capillary may contact and damage a ball bond which has been previously made at an adjacent bond pad. One method for resolving this problem is to use a wire bonding capillary with a non-circular face. This type of approach is shown, for example, in U.S. Pat. No. 5,544,804 issued to Test et al. (hereinafter "Test"). A capillary made per the invention disclosed in Test may be referred to as a BowTI.TM. capillary.
In a wire bonding machine, two BowTI.TM. capillaries may be employed. One capillary is used to make the bonds in the X direction of a given package and the other capillary is used to make the bonds in the Y direction of the package.
A problem arising from the use of capillaries having non-circular faces is the need for precise alignment of the longitudinal axis of the capillary face along either the X or Y axis of the lead frame, or along the longitudinal axis of a target lead, as necessary. Precise alignment of non-circular capillaries is especially difficult due to the relatively small size of a typical capillary face (e.g., 4-8 mil).
Further, with respect to non-circular capillary faces, precise alignment of the longitudinal axis of the capillary face during installation of the capillary into the transducer of a wire bonding machine is difficult. Moreover, it is difficult to accurately rotate the capillary to a precise angular alignment in which the longitudinal axis of the capillary face is offset from either the X or Y axis of the lead frame by a precise angular amount. It is difficult to check the alignment of the capillary at installation or during or after rotation of the capillary. Improper alignment of the capillary can lead to defective wire bonds during the manufacturing process.
In addition to the problems noted above with respect to alignment of the capillary face, the capillary must also be aligned longitudinally, such that a predetermined length of the capillary extends in the direction underneath the transducer. This distance must usually be set using calibrated tools.